The invention pertains to an interface between the exhaust gas outlet of a gas turbine and the inlet of an internally insulated exhaust gas diffuser. The gas turbine referred to in this application is of the type generally used in power generation.
In constructing the power turbine system, the exhaust from the gas turbine would be routed through a diffuser on its way to being routed through other equipment by way of various valves in the exhaust stream. Exhaust diffusers are either internally insulated (i.e. the structural shell plate is protected from hot exhaust by internal insulation and liner system) or externally insulated (i.e. structural shell plate is exposed to hot exhaust.) The externally insulated equipment is considered to suffer from several deficiencies vis a vis internally insulated equipment. Namely, the internally insulated equipment is considered to be more efficient, to last longer in the field, and enjoy assembly benefits such as the ability to be shipped in at higher levels of assembly. The gas turbine is typically externally insulated while in many situations its remaining equipment is preferably internally insulated.
The exhaust outlet from the gas turbine has to be connected to the inlet of the diffuser in such a way to provide a seal so that no exhaust leaks to the outside or ambient air through the connection. This sealing relationship must be maintained throughout the operating conditions of the power generation system. By way of example, the interface between the exhaust gas outlet and the diffuser can go from temperatures of subzero degrees F. to over 1200.degree. F. in the matter of a few minutes such as when a system located in a cold climate is started. Likewise, interruptions in operation of the gas turbine such as shut downs for maintenance, etc. will cause the interface to cool from elevated operating temperatures to the ambient temperature. These stresses of expanding and contracting must be repeatedly accommodated over the life of the interface.
Prior interfaces between the gas turbine and diffuser relied on complicated gasketing arrangements to provide a gas tight seal that would survive over repeated cycling. The provision of this gasketed seal required precise machining, numerous parts and involved field assembly. As a result, the seal area was difficult to assemble, and expensive, both from a parts manufacture and assembly standpoint. Small deviations in the machining could also result in a unsatisfactory seal.
Previously expanding bell type seals have been used experimentally in other connections in the exhaust path such as connecting exhaust plenums. Seals in these areas are not subject to the same stressful environment as immediately downstream of the turbine and before the diffuser. Results obtained from further downstream components are not always applicable to upstream situations.